Moulding mixture for producing casting moulds for metalworking

Abstract

The invention relates to a moulding mixture for producing casting moulds for metalworking, a process for producing casting moulds, casting moulds obtained by the process and also their use. To produce the casting moulds, a refractory mould raw material and a binder based on water glass are used. A proportion of a particulate metal oxide selected from the group consisting of silicon dioxide, aluminium oxide, titanium oxide and zinc oxide is added to the binder. Particular preference is given to using synthetic amorphous silicon dioxide as metal oxide.

1. Moulding mixture for producing casting moulds for metalworking, comprising at least:
 a refractory mould raw material; and 
 a binder comprising
 water glass, the weight thereof being calculated based on a solids content of 30 to 60% by weight of an aqueous water glass composition, and 
 a particulate synthetic amorphous silicon dioxide, wherein the binder is cured at 100° C. to 300° C.; and 
 wherein the binder is present in the moulding mixture in an amount of less than 5% by weight, or, if hollow microspheres are present in the mould raw material, the binder is present in an amount less than 20%, by weight. 
 
 
     
     
       2. Moulding mixture according to  claim 1 , characterized in that the synthetic amorphous silicon dioxide is selected from the group consisting of precipitated silica and pyrogenic silica and mixtures thereof. 
     
     
       3. Moulding mixture according to  claim 1 , characterized in that the water glass has an SiO 2 /M 2 O ratio in the range from 1.6 to 4.0 where M represents sodium ions and/or potassium ions. 
     
     
       4. Moulding mixture according to  claim 1 , characterized in that the water glass has a solids content of SiO 2  and M 2 O in the range from 30 to 60% by weight. 
     
     
       5. Moulding mixture according to  claim 1 , characterized in that the particulate synthetic amorphous silicon dioxide comprises from 2 to 60% by weight, based on the binder. 
     
     
       6. Moulding mixture according to  claim 1 , characterized in that the mould raw material comprises at least a proportion of hollow microspheres. 
     
     
       7. Moulding mixture according to  claim 6 , characterized in that the hollow microspheres comprise hollow aluminum silicate microspheres and/or hollow glass microspheres. 
     
     
       8. Moulding mixture according to  claim 1 , characterized in that the mould raw material comprises at least a proportion of glass granules, glass beads and/or spherical ceramic bodies and mixtures thereof. 
     
     
       9. Moulding mixture according to  claim 1 , characterized in that the mould raw material comprises at least a proportion of mullite, chromium ore sand and/or olivine and mixtures thereof. 
     
     
       10. Moulding mixture according to  claim 1 , further comprising an oxidizable metal and an oxidant. 
     
     
       11. Moulding mixture according to  claim 1 , further comprising a platelet-like lubricant. 
     
     
       12. Moulding mixture according to  claim 11 , characterized in that the platelet-like lubricant is selected from the group consisting of graphite and molybdenum sulphide and mixtures thereof. 
     
     
       13. Moulding mixture according to  claim 1 , further comprising at least one organic additive which is solid at room temperature. 
     
     
       14. Moulding mixture according to  claim 1 , further comprising at least one silane. 
     
     
       15. Process for producing casting moulds for metalworking, which comprises the steps:
 producing a moulding mixture according to  claim 1 ; 
 moulding the moulding mixture; and 
 curing the moulding mixture by heating the moulding mixture to temperature in the range from 100° C. to 300° C. to produce the cured casting mould. 
 
     
     
       16. Process according to  claim 15 , characterized in that heated air is blown into the moulding mixture for curing. 
     
     
       17. Process according to  claim 15 , characterized in that the heating of the moulding mixture is effected by the action of microwaves. 
     
     
       18. Process according to  claim 15 , characterized in that the casting mould is a feeder. 
     
     
       19. Casting mould obtained by a process according to  claim 15 , wherein the casting mould has high strength immediately after production and high stability in the presence of relatively high humidity. 
     
     
       20. A process for the casting of a metal product comprising
 preparing a casting mould using the process of  claim 15 , and introducing liquid metal into the casting mould to produce the cast metal product. 
 
     
     
       21. Process according to  claim 15 , characterized in that the curing is carried out for less than 5 min. 
     
     
       22. Process according to  claim 15 , characterized in that heated air is blown into the mould during the curing process. 
     
     
       23. Process for producing casting moulds for metalworking, which comprises the steps:
 producing a moulding mixture comprising at least:
 a refractory mould raw material, and 
 a binder comprising
 water glass, the weight being calculated based on a solid content of 30 to 60% by weight of an aqueous water glass composition, and 
 a particulate synthetic amorphous silicon dioxide, wherein the binder is present in the moulding mixture in an amount of less than 5% by weight, or, if the moulding mixture comprises hollow microspheres, said binder is present in the moulding mixture in an amount of less than 20% by weight; 
 
 
 moulding the moulding mixture;
 and curing the moulding mixture for less than 5 min by heating the moulding mixture to a temperature in the range from 100 to 300° C. to produce the cured casting mould, wherein during curing, heated air is blown into the mould.